Photon Sciences, Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607, Hamburg, Germany.
Bayerisches Geoinstitut, University of Bayreuth, Universitätsstraße 30, 95440, Bayreuth, Germany.
Nat Commun. 2018 Nov 15;9(1):4789. doi: 10.1038/s41467-018-07265-z.
Modelling of processes involving deep Earth liquids requires information on their structures and compression mechanisms. However, knowledge of the local structures of silicates and silica (SiO) melts at deep mantle conditions and of their densification mechanisms is still limited. Here we report the synthesis and characterization of metastable high-pressure silica phases, coesite-IV and coesite-V, using in situ single-crystal X-ray diffraction and ab initio simulations. Their crystal structures are drastically different from any previously considered models, but explain well features of pair-distribution functions of highly densified silica glass and molten basalt at high pressure. Built of four, five-, and six-coordinated silicon, coesite-IV and coesite-V contain SiO octahedra, which, at odds with 3 Pauling's rule, are connected through common faces. Our results suggest that possible silicate liquids in Earth's lower mantle may have complex structures making them more compressible than previously supposed.
模拟深部地球液体涉及的过程需要了解其结构和压缩机制的信息。然而，对于深部地幔条件下硅酸盐和二氧化硅（SiO）熔体的局部结构及其致密化机制的了解仍然有限。在这里，我们使用原位单晶 X 射线衍射和从头算模拟报告了亚稳态高压二氧化硅相——柯石英-IV 和柯石英-V 的合成和表征。它们的晶体结构与任何以前考虑过的模型都有很大的不同，但很好地解释了高度致密化的二氧化硅玻璃和高压玄武岩的配分函数特征。由四个、五个和六个配位的硅组成的柯石英-IV 和柯石英-V 包含 SiO 八面体，与 3 个鲍林规则相反，它们通过共面连接。我们的结果表明，地球下地幔中可能存在的硅酸盐液体可能具有复杂的结构，使它们比以前认为的更具可压缩性。
